Oat cell carcinoma of the lung is being treated by our group with high dose combination chemotherapy and relapsed adult acute leukemia with chemotherapy and total body irradiation. In order to protect the patient against myelosuppression as a consequence of massive cytoreductive therapy autologous marrow collected and stored previously, is being infused after therapy. In the light of this program we propose in this grant studies in mice with the following objectives: 1) to test the quality and quantity of stem cells exposed to chemotherapy; 2) to test the effect of combination chemotherapy used as cytoreductive therapy prior to marrow rescue on the infused hemopoietic stem cells; 3) to determine the value of in vitro colony formation by hemopoietic cells as monitor system for pluripotent hemopoietic stem cells in conditions in which stem cells have been exposed to chemotherapy.